Carbohydrates are synthesized by plants through photosynthesis. Animals ingest carbohydrates for use as a source of energy. Besides monosaccharides, oligosaccharides, polysaccharides, and other such saccharides, carbohydrates also include saccharide analogs such as cyclic polyhydric alcohols, amino sugars, and the like.
Glucose, which is representative of carbohydrates, is expressed by the chemical formula C6H12O6. Complete oxidation of glucose results in liberation of 24 electrons per molecule of glucose, with production of carbon dioxide gas and water. These 24 electrons are utilized as a source of energy within the animal body.
Thermodynamic calculations indicate that glucose possesses 2872 kJ of energy per 1 mole, or 4.43 W·hr per 1 gm. This is as much or greater than the weight energy density of 3.8 W·hr/gm of the metallic lithium employed at the negative electrode of the lithium battery which is well known as a high energy density battery.
There are only two methods which have been discovered to date for utilization of the energy possessed by carbohydrates. One is utilization of the thermal energy produced by direct combustion of carbohydrate in air, and the other is utilization in the form of the chemical energy produced by action of any of some 12 or more types of oxidase present within the body of an animal which has consumed carbohydrate (Albert et. al., Essential Cell Biology (Garland Publishing, Inc.), 107 (1997)).
This is to say that a method that would allow the chemical energy which carbohydrates possess to be effectively utilized directly as electrical energy has yet to be discovered.